Apr 25, 2021
Linear bed foot method determines fertilizer needs for plastic mulch crops

In the Mid-Atlantic Commercial Vegetable Production Recommendations, fertilizer recommendations are given on a per acre basis. For crops grown on plastic mulch, the most common bed spacing between rows is used and recommendations are based on linear bed foot (LBF) values.

The LBF system can be used to express fertilizer rates for any fertilizer delivery method with mulched beds, including production systems using bed placed fertilizers. In the production systems that rely on the drip irrigation system to deliver water and fertilizers, the LBF fits closely because growers already know the total length of drip tubing in an acre. LBF can also take into account areas for drive rows used for sprayers such as in watermelons or cantaloupes.

The following are LBF values that fertilizer recommendations are based on in the Mid-Atlantic on plastic mulch:

  • Cucumbers: 7,260 linear bed ft./acre (6-foot bed spacing, 2 rows per bed)
  • Eggplant: 7,260 linear bed ft./acre (6-foot bed spacing, one row per bed)
  • Muskmelons and Mixed Melons: 7,260 linear bed ft./acre (6-foot bed spacing, 1 row per bed)
  • Peppers: 7,260 linear bed ft./acre (6-foot bed spacing, 2 rows per bed)
  • Summer Squash: 7,260 linear bed ft./acre (6-foot bed spacing, 2 rows per bed)
  • Tomatoes: 7,260 linear bed ft./acre (6-foot bed spacing, one row per bed)
  • Watermelons: 6,222 linear bed ft./acre (7-foot bed spacing, one row per bed)
  • If bed widths are different then adjustments should be made to fertilization rates and if unplanted drive rows are used then rates per acre will also be reduced.

To make these adjustments you need to know the following:

  • Real-estate acre: Farm land (land area) that occupies 43,560 square feet. This term also may be called “gross acre” and refers to the land area used for crop production, including the cropped land plus the land used for drive rows, field rows roads and drainage ditches.
  • Cropped area: The portion of the real-estate acre used solely for crop production. Alternatively, the cropped area is the land remaining after uncropped land, such as drive or access roads, have been subtracted from the real-estate area. If the entire area is used for crop production, then the cropped area is equal to the real-estate area. Otherwise, the cropped area is less than the real-estate area.

Some watermelon examples:

  1.  Crop is grown on 8-foot bed centers, not 7-foot: Total bed feet would be 43,560/8 or 5,445 LBF.Fertilizer would be reduced by 6,222-5,445=777/6,222 = 12.5% so if the recommendation is 125 lbs of N per acre you would reduce that by 16 lbs (109 lbs N per acre).
  2. A drive row is placed after every 8 beds on 7 foot centers. The cropped area is 8/9 or 89%. So the LBF would be 11% less. If the recommendation is 125 lbs/acre N, then the actual amount applied would be 0.89*125 or 111 lbs of N per acre.

For more information on Linear Bed Foot for fertilizer recommendations see the University of Florida fact sheet. Much of the information used in this article was taken from this publication.

Gordon Johnson, Extension Vegetable & Fruit Specialist

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